Quantification of reduced and oxidized coenzyme Q10 in supplements and medicines by HPLC-UV

Coenzyme Q10 (CoQ10) supplements are widely used because of their antioxidant and anti-inflammatory effects, especially in the management of cardiovascular diseases. The latest pharmaceutical approach to increase CoQ10 bioavailability and efficiency is the formulation of its reduced form. Regardless of the growing number and usage of CoQ10 preparations, their analytics and quality control is inadequate, neglecting interconversion between the two CoQ10 forms. Therefore, this study proposes a HPLC-UV method for the simultaneous quantification of both reduced and oxidized coenzyme Q10, as well as total CoQ10, as a sum of its individual forms. The suitability of the developed method was confirmed by two additional approaches for total CoQ10 determination - its total reduction and oxidation, differing from the proposed procedure only in the final stage of sample preparation. The results for total CoQ10 content were consistent between the three procedures and also with the official USP method for total CoQ10 determination. The proposed method was applied to 13 dietary supplements and medicines in the form of soft- and hard-shell capsules, revealing the co-existence of both CoQ10 forms in 85% of the tested preparations. CoQ10 forms that were undeclared accounted for up to 75% of the CoQ10 content, which is overlooked by current official methods that evaluate only the total CoQ10 content. This validated HPLC-UV method for the unequivocal quantification of reduced and oxidized CoQ10 is therefore appropriate for the routine analysis of CoQ10 preparations in quality control laboratories, as well as for stability studies, and is suggested to be adopted as an official method.